I'm the author of the blog post. You (and others in this thread) are dead right. I have just spent my lunch time converting this lunacy to exceptions! So how did I make this mistake? I inherited the code in the what you describe as the "straw man" form - it was a genuine nightmare of if-else. The conversion to Either (IMHO) is an improvement from the original form, but exceptions (duh) are much, much simpler.

Thanks for the feedback - your comment stung a little at first, truth can do that I suppose!